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Rick,
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<div>I agree that you have much more flexibility to try different beamformer designs, detection algorithms, interference mitigation techniques, superresolution, calibration correction, etc. if you store and operate on the accumulated cross products (correlation
matrices). However, you give up the ability to do fine resolution spectral processing. You are stuck with the coarseness of the correlator's frequency channelization. I don't know how problematic this is for some applications, such as pulsar searches, where
fine spectral resolution may be needed.</div>
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<div>Brian</div>
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<div>On May 20, 2013, at 6:38 AM, Anish Roshi wrote:</div>
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Yes indeed. We can form images with beams with different optimization if the correlations are recorded.<br>
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Anish<br>
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<div class="gmail_quote">On Sun, May 19, 2013 at 9:57 AM, Rick Fisher <span dir="ltr">
<<a href="mailto:rfisher@nrao.edu" target="_blank">rfisher@nrao.edu</a>></span> wrote:<br>
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Brian, Karl,<br>
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In trying to understand the ASKAP data processing architecture, I'm<br>
beginning to understand the fundamental importance of saving the<br>
cross-products between array element outputs in our own PAF data<br>
processing. In forming beams you throw away a lot of information in the<br>
array's field of view that can be recovered only by forming many beams<br>
with very close spacing (much closer than HPBW/2). This has important<br>
consequences for the sensitivity to point sources, as in the search for<br>
pulsars. Hence, I would suggest that the most important archived outputs<br>
from your signal processor are the cross-products rather than formed<br>
beams. For a given data storage volume, there's more information in the<br>
cross-products than in the formed beam outputs. In some respects, the<br>
"beam" concept is a holdover from a waveguide feed where there's only one<br>
output, and most of the information in the focal plane is reflected back<br>
into the sky.<br>
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Rick<br>
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